Double Asymmetric Duty Modulation With Wide-Operating-Range Multiobjective Optimizations in DAB-Based Electric Vehicle Applications

Due to high power density, simple control scheme and bidirectional power transmission ability, dual-active-bridge (DAB) converter has been widely applied into electric vehicle (EV) applications. For conventional phase-shift modulations, fixed 50% duty-ratio of driving signals will lead to limited zero-voltage-switching (ZVS) range and excessive current level. Meanwhile, root mean square (RMS) current optimization will also result in restricted ZVS range. Subsequently, in this article, double asymmetric duty modulation (DADM) is introduced to solve aforementioned questions. On the one hand, operation principle, typical modes demonstrations are displayed. Considering non-linear characteristics of junction capacitance Coss, ZVS performance under different DADM modes is analyzed in detail and corresponding ZVS boundary can be established. Simultaneously, effect of dead time is also illustrated. On the other hand, for efficiency promotion strategy, a wide-operating-range multi-objective optimization method based on non-dominated sorting genetic algorithm II (NSGA-II) is proposed to optimize RMS current and peak current simultaneously under all switches ZVS operations. Meanwhile, current pareto-optimal curves under numerous operation conditions will be established. Through comprehensive comparisons among existing modulations, peak current and RMS current could be reduced at more than 10%. ZVS range could be extended more than 33%. As a result, efficiency value could be optimized more than 1.1% especially at light-load condition. Finally, a DAB prototype is established and effectiveness and correctness of proposed method can be proved.